Twins born as a result of fertility treatment are at greater risk of serious illness or dying in the first three years of their life than those who are conceived naturally, a study suggests.

Siblings born together after in vitro fertilisation (IVF) stay an average of four days longer in hospital after birth and are far more likely to be admitted to a neo-natal intensive care ward.

They are more than twice as likely to die just before or just after birth, although the reasons for this are not clear, researchers at the universities of Western Australia and Oxford said.

They said that couples undergoing fertility treatment should be aware of the risks and advised them to consider “single-embryo transfer”, where only one embryo is implanted into the womb at a time.

Between 20 and 30 per cent of deliveries after fertility treatment are twins, compared with approximately 1 per cent of natural conceptions. Couples who conceive through IVF are much more likely to have non-identical twins because two or more embryos are usually implanted in the womb.

The Human Fertilisation and Embryology Authority has repeatedly warned of the risks of multiple pregnancies for both mother and baby and now urges clinics not to transfer more than one embryo per treatment cycle.

Multiple-birth babies are more likely to be born prematurely or underweight. They are less likely to survive and more likely to suffer breathing problems or defects such as cerebral palsy, impaired vision or congenital heart disease.

Mothers bearing twins also face an increased risk of heavy bleeding, miscarriage, pre-eclampsia — a complication linked to high blood pressure — and diabetes.

The study, reported in the journal Human Reproduction, examined hospital admissions for all twin children born in Western Australia between 1994 and 2000, whether as a result of fertility treatment or natural conception. In that period, 700 twins were born after fertility treatment and 4,097 after natural conception.

However, to ensure a fair comparison, the twins born following IVF were compared with 1,240 naturally conceived, non-identical twins of different sexes. The IVF twins had a greater risk of adverse outcomes. They also stayed longer in hospital after birth — an average of 12 days compared with eight.

IVF twins had a two-thirds higher risk of being admitted to intensive care and were more likely to return to hospital during their first three years of life. This was after taking into account factors which may have swayed the results, including year of birth, maternal age and the number of times that a woman had given birth.

Michèle Hansen, who led the research at the Telethon Institute for Child Health Research in Perth, said: “Couples undergoing fertility treatment should be aware that, in addition to the known increased . . . risks associated with a twin birth, ART [assisted reproductive technology] twins are more likely than spontaneously conceived twins to be admitted to . . . intensive care and to be hospitalised in their first three years of life.”

She said that the underlying causes of parental infertility may have increased the risks of certain health problems. People who became parents after a long period of trying unsucessfully might also have been more likely to take their children to hospital at the first sign of minor health problems.

Peter Braude, a spokesman for the Royal College of Obstetricians and Gynaecology and head of the department of women’s health at King’s College London, said: “This study will hopefully remind people about the risks of multiple births due to IVF treatment.

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